The present invention relates to a magnet system having a magnet coil surrounded by an insulating frame.
Magnet coils may be used with fuel injectors of fuel supply systems for internal combustion engines. In the case of magnet coils of solenoid valves, there is a general requirement that the switching dynamics be improved to achieve short switching times and to prevent excessive heating of the electromagnet through good heat dissipation.
Published German Patent Application No. 197 15 234 discloses a direct injection fuel injector having magnetic control for accumulator injection systems. The fuel injector includes in each valve housing a supply line which leads to a spring-loaded nozzle needle and which may be closed by a control piston having a valve function; also included is a nozzle needle spring which is supported in a spring space and presses the nozzle needles onto their needle seats. A control space is provided on the rear side of the control piston, which is under system pressure. The control space is connectable to a relief line by a solenoid valve, and simultaneously with the injection, the closing of the supply line leading to the nozzle needle may be canceled by a high-pressure valve situated on the control piston. Furthermore, a throttled line connection is provided as a bypass between the supply line and the relief line in the fuel injector, the line connection containing a leakage valve mechanically connected to the solenoid valve, so that the line connection may be interrupted by this valve during the injection.
Published European Patent Application No. 657 642 discloses a fuel injection system for internal combustion engines. The fuel injection system for internal combustion engines includes a high-pressure collecting space which may be filled by a high-pressure fuel pump, and which has high-pressure lines leading away from it to the individual injectors. Control valves are used in the individual high-pressure lines to control the high-pressure injection at the injectors, and an additional accumulator space is provided between these control valves and the high-pressure collecting space. To prevent the high system pressure from being applied continuously to the injectors, the control valve is designed so that it closes its connection to the accumulator space during the injection pauses at the injectors, and it notches up a connection between the injectors and a relief space. The control valve is designed as a 3/2-way valve in which a piston-shaped valve member is actuated by an electric actuator magnet which acts on its one end face opposite a compression spring supported between the housing and a spring plate on the valve member. The electric actuator magnet receives electric power from a control unit.
Published German Patent Application No. 197 14 812 discloses a conventional magnet coil. The conventional magnet coil is formed by a winding wire wound onto a winding carrier. Such a magnet coil is used, e.g., in solenoid valves, which are used in fuel pumps of internal combustion engines to control the pump delivery rate and the course of delivery. During operation, fuel under a high pressure flows around the solenoid valves at least to some extent. The magnet coil must be encapsulated to prevent it from coming in contact with the fuel. In the case of common-rail fuel injection systems or pump-nozzle units in particular, solenoid valves having extremely short switching times are needed. The short switching times result in heating of the magnet coil during operation, and therefore dissipation of heat at the magnet coil must be ensured, because a thermal burden on the coil during operation is not desirable.
A frameless magnet coil including a winding accommodated in a magnet pot is known in the art. The winding is formed in particular from baked enamel wire, which is provided with a coating to ensure cohesion of the winding of the magnet coil. The magnet coil winding is situated in a toroidal cup. Interspaces between the coil and the magnet pot are reduced significantly by securing the coil and pot using a casting compound. This also yields an improvement in dynamics and in heat dissipation. On the other hand, problems occur with respect to handling, correct positioning and the risk of an electric short circuit between the coil wire and the magnet pot, as well as the risk of cavities forming in the casting compound. Furthermore, leakage may occur at the outlet of the magnet pot due to an undefined position of the coil wire, so that this arrangement has some disadvantages.
In accordance with an embodiment according to the present invention, by using an extremely thin-walled coil insulating frame, it is possible to use magnets which have a very small defined interspace between the bobbin and the magnet pot, so that an extremely miniaturized embodiment of electromagnets becomes possible. Through the embodiment according to the present invention, handling of very small magnet coils having an average diameter of less than 5 mm to 6 mm may be facilitated; furthermore, the magnet coils surrounded by a thin-walled bobbin may be positioned inside the magnet pot with very high precision. Due to the arrangement of the coil insulating frame in the magnet pot, there is a uniform gap for the introduction of casting compound, so the casting compound flows uniformly within the gap, and unwanted cavities cannot develop in the casting compound, nor is there any accumulation of material or areas having unacceptably thin walls. A non-uniform distribution of casting compound in the annular gap between the electromagnet and the magnet pot has a negative effect on the dissipation of heat and should be avoided.
Short-circuiting between the coil and the magnet pot is prevented by using coil insulating frames having thin walls, e.g., walls less than 200 xcexcm to 300 xcexcm thick.
In one embodiment of the proposed thin-walled coil insulating frame, tubular projections may be mounted on it, permitting easier insertion of contact prongs. Furthermore, the space reserved by the thin-walled coil insulating frame may be filled with a casting compound that hardens.
Use of a thin-walled coil insulating frame prevents damage to components during assembly or handling of the components; such damage could have a considerable effect on the subsequent functionality of an assembled electromagnet coil.
The present invention permits an interaction of well-defined, uniform interspaces between the coil and the magnet pot, so that casting/injection of a free-flowing compound is facilitated, resulting in magnets that are optimized with regard to dissipation of heat.